Drill, baby, drill -- on Mars (pictures)

As the Curiosity rover prepares to drill into the Martian surface for the first time, more signs point to a watery past.

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Curiosity prepares to drill

In the coming days, five months after landing on the red planet, NASA's Curiosity rover will maneuver carefully into position as it approaches the "John Klein" site inside the Gale Crater, the place at which Curiosity will drill into the Martian surface for the first time.

NASA says the selected target location offers a bounty of diverse and unexpected features for exploring the mineral and chemical composition of the surface of Mars, including mineral veins, nodules, cross-bedded layering, a lustrous pebble embedded in sandstone, and possibly some holes in the ground.

"These veins are likely composed of hydrated calcium sulfate, such as bassinite or gypsum," said ChemCam team member Nicolas Mangold of the Laboratoire de Planétologie et Géodynamique de Nantes in France. "On Earth, forming veins like these requires water circulating in fractures."

This image was taken by Curiosity's Navcam on Sol 159 of the journey, January 16, 2013.

'John Klein' site selected for Curiosity's debut drill

This annotated view, captured on January 10, shows the patch of veined, flat-lying rock known as "John Klein" where drilling will soon commence, as seen by the rover's Mast Camera telephoto lens.

The area is rich with geologic detail and features of interest, says NASA. Fractures and veins, along with small, spherical concentrations of minerals called concretions will all be of interest to Curiosity's spinning drill. The scale bar on the left image is 19.7 inches long, with the three enlarged areas on the right highlighting sections about 4 inches across.

Enlargement A shows a high concentration of ridge-like veins protruding above the surface. Some of the veins have two walls and an eroded interior. Enlargement B shows that in some portions of this feature, there is a horizontal discontinuity a few centimeters or inches beneath the surface. The discontinuity may be a bed, a fracture, or potentially a horizontal vein. Enlargement C shows a hole developed in the sand that overlies a fracture, implying infiltration of sand down into the fracture system.

'Shaler' unit's evidence of stream flow

Inclined layering known as cross-bedding appears in an outcrop nicknamed "Shaler" on a scale of a few tenths of meters. NASA says the cross-bedding evident in the Shaler location is indicative of sediment transport in stream flows, hinting at past flowing water. Currents may have molded these sediments into small underwater rifts or dunes that then move downstream. When exposed in cross-section, evidence of this migration is preserved as strata that are steeply inclined relative to the horizontal -- thus the term "cross-bedding."

Wind formation has been ruled out here because the grain sizes are coarse enough that the formations are formed by currents, not by wind, NASA believes.

Veins in 'Sheepbed' outcrop

A rock outcrop at a location nicknamed "Sheepbed" shows well-defined, whitish veins that NASA believes to be calcium sulfate.

On Earth, these veins form when water flows through fractures in rock, depositing minerals along the sides of the fracture and eventually forming a vein. These veins are Curiosity's first look at minerals that formed within water that percolated within a subsurface environment.

Geologic diversity at 'John Klein'

Images of Curiosity's first drilling site, "John Klein," show the diversity of rock types available to NASA from which the rover team could choose to sample. Enlargements of the rocks seen on the right show the rock types, including a "bread crusted" rock in enlargement A, whose surface is fractured in a polygonal pattern. This generally reflects a differential change in volume of a rock, with the outer part expanded relative to the interior.

Enlargement B shows both light-toned veins and dark spots that show the relief of concretions, and enlargement C shows an exotic black rock that is similar in shape to more distant, dark rocks found higher in the local stratigraphy, which NASA believes was ejected to the current site by a crater-excavating impact.

Near the 'John Klein' drill site

'Yellowknife Bay' veins and concretions

In enlargements taken by the Mast Camera of NASA's Curiosity Mars seen here on the right, white arrows point to veins, and black arrows point to the small spherical concentrations of minerals called concretions in a low-lying dry stream bed named "Yellowknife Bay." Both veins and concretions strongly suggest precipitation of minerals from water. Curiosity's team decided to focus here for a first drilling target because orbital observations have shown fractured ground that cools more slowly each night than nearby terrain types do.

Veins in rocks on Mars and Earth

Comparing the similarities of what has been observed thus far on Mars, and more familiar and better understood geologic features on Earth, this set of images shows the likeness between sulfate-rich veins seen on Mars by NASA's Curiosity rover to sulfate-rich veins seen here on our planet.

The view on the left is a mosaic showing two shots from the remote micro-imager on Curiosity's Chemistry and Camera instrument of
a view of "Sheepbed" rock in the "Yellowknife Bay" area of Mars. The sulfate-rich veins are the light-colored veins about 1-5 millimeters wide, while the image on the right is from the Egyptian desert on Earth, with a pocket knife shown for scale.

Curiosity's traverse into new terrain

This image maps the traverse of NASA's Mars rover Curiosity within Gale Crater from "Bradbury Landing" to its current location at "Yellowknife Bay," with an inset documenting a change in the ground's temperature during the rover's travels.

Between December 7 and December 8, Curiosity breached a terrain boundary, crossing into lighter-toned rocks which correspond to high thermal inertia values observed by NASA's Mars Odyssey orbiter. The green dashed line marks the boundary between the terrain types.

The inset graphs the range in ground temperature recorded each day by the Rover Environmental Monitoring Station on board Curiosity. The arrival onto the lighter-toned terrain corresponds with an abrupt shift in the range of daily ground temperatures marking the rover's arrival at exposed and stratified bedrock.

December 8 marked the arrival at the Shaler Unit where scientists saw cross-bedding that is evidence of water flows. December 11 marked the arrival into the area called "Yellowknife Bay," where sulfate-filled veins and concretions were discovered in the Sheepbed Unit, along with much finer-grained sediments. The thin dashed line is based on previous Odyssey thermal inertia mapping in 2005 by Robin Fergason and co-authors.